I. Field of Invention
This invention relates to an apparatus, sensor, and/or method for monitoring the state of an ion-exchange material and in certain aspects the use of that information for water softener control.
II. Background of the Invention
Some water softeners are configured to pass hard water through an ion exchange resin or mineral bed to remove hardness ions from the water. The ion exchange resin or mineral, to a limited extent, also removes dissolved iron through an ion exchange process. The ion exchange resin or mineral bed is recharged to regenerate its hardness and iron removal capability by passing brine through the resin or mineral bed and by backwashing.
The ion-exchange resin or mineral bed is typically regenerated with a brine of NaCl when its ion-exchange capacity is exhausted. An important aspect of the control of a water softener is the determination of when to initiate the regeneration. For most efficient utilization of salt for regenerating and water for rinsing, it is advantageous to initiate regeneration as soon as breakthrough is detected, but existing analytical instruments for measuring hardness in the water are notoriously expensive and time-consuming. The alternative to detecting breakthrough is to make a conservative estimate of when resin exhaustion will occur with calculations based on assumptions of the hardness of the feed water and the quantity of water that has passed through the resin bed. In one approach total daily water usage is estimated and a timer initiates regeneration after the lapse of a certain number of days. The timer does not distinguish days when there is no flow of water from days when there is a high flow, and the softener might be regenerated when little or none of its capacity has been utilized or it might be regenerated long after breakthrough has occurred, resulting in the passage of untreated hard water.
Another approach is to use a flow totalizer, which measures the quantity of water that has been processed by the softener and initiates regeneration when a preselected quantity of water has been processed. Use of the flow totalizer usually results in better salt economy than the timer, but that approach does not account for variation in the hardness of the source water or deterioration in the ion-exchange capacity as the resin ages.
In another approach the electrical conductivity of the resin bed is used to determine the need for regeneration. Utilization of the conductivity measurement is based on the fact that calcium ions are more tightly held by the resin, and consequently the resin is less conductive in the calcium form than in the sodium form. However, the measurement of resin bed conductivity is confounded by two problems. First, the continuity of current flow between resin beads is through point contacts between spheres, so the measured conductivity through the path of resin beads is much lower than the conductivity of the individual beads. Second, the solution between the beads is also conductive, so changes in the conductivity of the solution will affect the measured conductivity by providing a shunt through which electric current flows. A common approach to alleviating these problems is to install multiple pairs of electrodes in the resin bed and compare the measurements. These imbedded probes still suffer from the fact that they rely on an indirect measurement and do not directly detect breakthrough of calcium.
Additional apparatus and methods for detection of breakthrough or exhaustion of a water softener resin are needed.